A three-phase motor drive control circuit with a Hall element controls the timing of motor driving based on a motor rotational position signal produced in the Hall element. In addition, some three-phase motor drive control circuits generate a rotation number pulse signal, so-called FG signal, indicating the number of rotations from the rotational position signal and adjust the timing of motor driving using the number of rotations information obtained from the FG signal (see, for example, Japanese Patent Laying-Open No. 6-169586 (Patent Document 1)). FIG. 6 is a circuit diagram of a motor device including a conventional motor drive control circuit. FIG. 6 shows a motor device 101 including such a motor drive control circuit 102.
This motor device 101 includes Hall elements HU, HV, HW detecting a position of a rotor of a motor to output rotational position signals, motor drive control circuit 102 outputting a control signal based on these rotational position signals and a command from a motor control command portion (not shown), and a power driver 103 supplying driving current to coils LU, LV, LW of the motor in response to the control signal from motor drive control circuit 102. It is noted that the rotational position signal is a three-phase sinusoidal signal formed of differential U-phase rotational position signals HU+ and HU− output by Hall element HU, differential V-phase rotational position signals HV+ and HV− output by Hall element HV, and differential W-phase rotational position signals HW+ and HW− output by Hall element W. The phase difference between phases is 120°.
Motor drive control circuit 102 has a power driver control circuit 109, a rotation number pulse signal generation circuit 117, and a waveform shaping circuit 110 formed of U-phase, V-phase, W-phase comparators 111, 112, 113 provided at a stage prior to rotation number pulse signal generation circuit 117. Power driver control circuit 109 receives rotational position signals HU+, HU−, HV+, HV−, HW+, HW−, a command signal from the motor control command portion (not shown) and a rotation number pulse signal FG of rotation number pulse signal generation circuit 117 as described later to output a control signal to power driver 103. The command signal from the motor control command portion is input to power driver control circuit 109 through an input terminal TO. U-phase comparator 111 compares differential U-phase rotational position signals HU+ and HU− to output a pulse signal HU2 as the comparison result. V-phase comparator 112 compares differential V-phase rotational position signals HV+ and HV− to output a pulse signal HV2 as the comparison result. W-phase comparator 113 compares differential W-phase rotational position signals HW+ and HW− to output a pulse signal HW2 as the comparison result. The foregoing rotation number pulse signal generation circuit 117 combines pulse signals HU2, HV2, HW2 to generate rotation number pulse signal FG and output the rotation number pulse signal FG to power driver control circuit 109.
Here, U-phase, V-phase, W-phase comparators 111, 112, 113 have hysteresis, and the noise superimposed on rotational position signals HU+, HU−, HV+, HV−, HW+, HW− is removed if its magnitude is within a prescribed voltage width, that is, a hysteresis width. Thus, such a phenomenon, that is, chattering is prevented to some extent in that the outputs of comparators 111, 112, 113 become unstable to produce minute pulses when they are switched from a high level to a lower level or from a low level to a high level, and therefore, in rotation number pulse signal generation circuit 117 receiving them, generation of erroneous rotation number pulse signal FG can be suppressed.
Patent Document 1: Japanese Patent Laying-Open No. 6-169586